In recent liquid crystal display television receivers, real-timer digital signal processing for video signals has been frequently employed, and among the television signal processings a base-band video-signal processing which is performed in a digital fashion has been put to practical use in a form of IDTV. The conventional digital video-signal processing circuit is constructed as shown in FIG. 1. More specifically, a composite video signal output from a video detector (not shown) is converted into a digital signal by an analog to digital converter (A/D converter) 11 and then separated into a luminance signal Y and a chrominance signal C by a luminance/chrominance separator circuit (Y/C separator circuit) 12. The chrominance signal C is demodulated into color-difference signals, R-Y and B-Y by a color-difference demodulator circuit 13 and transferred to a matrix circuit 14. In the matrix circuit 14, the color difference signals R-Y and B-Y are added to the luminance signal Y from Y/C separator circuit 12. As a result, color signals, R, G and B are obtained. Then these color signals R, G and B are sent to a liquid crystal display section (not shown) to be displayed on a liquid crystal display panel.
The above liquid crystal display panel provides a low gradient. Therefore, if the above liquid crystal display panel is not used efficiently, a picture with an adequate contrast of light and shade is not available on the above liquid crystal display panel. In the above conventional video-signal processing circuit, the luminance signal Y obtained by Y/C separator circuit 12 is directly input to the matrix circuit 14, which generates color signals R, G and B corresponding to a level of the luminance signal Y. Therefore, in case that a picture is of an average brightness, the color signals R, G, B vary with a median level of the luminance signal Y as their median level. Hence a picture can be displayed with adequate contrast or with a high gradient on the liquid crystal display panel. In case that a picture is a bright scene or a dark scene, and the level of the luminance signal Y is high or low, the color signals R, G, B from the matrix circuit 14 incline towards a high level or a low level. In this case, the liquid crystal display panel is used inefficiently so that a picture with an inadequate contrast of light and shade is displayed on the display panel.